1. Field of the Invention
The present invention relates generally to combustion gas powered fastener driving tools, and more particularly to a fastener driving tool such as a tacker or nailer having a movable piston powered by the pressure of combustion of a mixture of air and fuel consisting of liquefied gas such as liquefied butane gas.
2. Description of the Prior Art
One known combustion gas powered fastener driving tool is disclosed in U.S. Pat. No. 4,403,722. The disclosed fastener driving tool includes ports located between the top and bottom dead centers of a movable piston for permitting combustion gases to flow from a combustion chamber to the outside of tool after the piston sliding within a cylinder moves past the ports under the pressure of combustion of an air and fuel mixture within the combustion chamber. Combustion of the air and fuel mixture proceeds downwardly from an upper side of the top dead center adjacent to a spark plug, toward an upper end face of the piston. This means that combustion of a part of the air and fuel mixture existing in the vicinity of the spark plug raises the pressure in the combustion chamber which will start moving the piston downwardly. In this instance, it is likely that a part of the air and fuel mixture located adjacent the upper end face of the piston follows the downward movement of the piston and is withdrawn from the ports to the atmosphere before it is combusted. The rate of fuel consumption of the conventional fastener driving tool is, therefore, relatively low. When the driving tool is used in a badly ventilated working place or site, the unburnt fuel gases withdrawn from the tool gradually accumulate in the working site and may explode if ignited.
The conventional fastener driving tool includes an electric fan disposed within the combustion chamber for thoroughly mixing air and fuel. With this arrangement, the fan is heated at high temperatures when the fastener driving tool is used continuously. These high temperatures tend to deteriorate the durability of various components of the electric fan, resulting in a malfunction of the electric fan.